Comparative marine biodiversity and depth zonation in the Southern Ocean: evidence from a new large polychaete dataset from Scotia and Amundsen seas

Lenka Neal,Adrian G Glover,Emma Sherlock,Madeleine J Brasier,Katrin Linse

doi:10.1007/s12526-017-0735-y

Lenka Neal, Adrian G Glover + Show 3 more

Open Access

https://doi.org/10.1007/s12526-017-0735-y

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Abstract

Based on a dataset of 16,991 and 307 morphospecies of polychaete worms collected from 58 epibenthic sledge deployments across the Scotia and Amundsen Seas, we show that the structures of their shelf, deep-shelf and slope communities are composed of distinct polychaete assemblages spanning regions with “high”, “intermediate”, and “low” biodiversity. Depth has been identified as the main factor structuring the polychaete communities in both seas, countering the prevalent notion of extended eurybathy of the Southern Ocean benthos. From an evolutionary perspective, this strong dissimilarity between shelf and slope fauna could be interpreted as evidence for survival in shelf refugias, rather than migration into deeper waters during glacial maxima. The previously unsampled Amundsen Sea is shown to be diverse, harbouring a high level of taxonomic novelty, with many species new to science. The polychaete community of the inner shelf in the Amundsen Sea (Pine Island Bay) has also been shown to be of deep-sea character, likely due to intrusion of the Circumpolar Deep Water onto the shelf. In the Scotia Sea, our data support the notion of relatively high biodiversity of waters around the South Orkney Islands, South Georgia, and Shag Rocks (all recently established as Marine Protected Areas) and depressed diversity in the extreme environment of Southern Thule.

Highlights

The deep Southern Ocean that surrounds the Antarctic continent is still largely an unexplored wilderness, where ocean expeditions routinely bring up samples in which the majority of species are new to science (e. g. Hilbig et al 2006; Brandt et al 2007a, 2007b)
About 25% were identified to a named species while the remaining were designated as Bcf.^ or morphospecies only, owing to poor specimen condition, lack of appropriate taxonomic references
In terms of sampling intensity, the pooled data show some evidence that the sites are approaching asymptote in terms of species numbers with the Amundsen Sea more exhaustively sampled than the Scotia Sea

Summary

Introduction

The deep Southern Ocean that surrounds the Antarctic continent is still largely an unexplored wilderness, where ocean expeditions routinely bring up samples in which the majority of species are new to science (e. g. Hilbig et al 2006; Brandt et al 2007a, 2007b). The deep Southern Ocean that surrounds the Antarctic continent is still largely an unexplored wilderness, where ocean expeditions routinely bring up samples in which the majority of species are new to science The remote and extreme environment of Antarctica and its surrounding Southern Ocean has attracted scientific exploration since the mid-nineteenth century, including early expeditions such as the HMS Challenger, RV Belgica, and RRS Discovery. It has historically been considered a species-poor environment, with diversity constrained by low temperatures, extreme seasonality of productivity, isolation by the Antarctic Circumpolar Current and the lack of enough Btime^ since the last glaciation for speciation and radiation to occur Taxonomic and biogeographic studies have tended to reinforce this point noting for example the

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